1. Field of the Invention
The present embodiments relate to an etchant and a method for fabricating an electric device including a thin film transistor using the same. More particularly, the present embodiments relate to an etchant that can provide a high quality display due to a high aperture ratio and high definition, and reduced register-capacitor signal delay (referred to as RC delay), and a method for fabricating an electric device including a thin film transistor using the same.
2. Description of the Related Art
In an active matrix liquid crystal display and an active matrix organic light emitting diode (OLED) display, a thin film transistor (TFT) is generally used as a switching device at each liquid crystal cell or each pixel.
Recently, there has been a tendency to increase the size of liquid crystal displays and organic light emitting diode (OLED) displays. Accordingly, there is a greater requirement for higher resolution. The larger liquid crystal displays and OLED displays with higher resolution necessarily require reduced RC delay. The reduced RC delay can be accomplished by minimizing resistance of wires.
In general, molybdenum (Mo) with resistivity of less than 12 μΩcm and aluminum (Al) with resistivity of less than 5.5 μΩcm are used as wire for a thin film transistor or an electrode. Since these metals have high resistivity, they tend to make it difficult to manufacture a larger liquid crystal display and OLED display with higher resolution. Accordingly, since copper (Cu) has resistivity of less than 2.2 μΩcm, it is being researched as an alternative wire and electrode.
However, copper can be applied to all of a gate electrode, a source electrode, and a drain electrode of a thin film transistor, but when it is applied to a gate electrode, it has poor adherence to a glass substrate where a thin film transistor is formed. In addition, when it is applied to a source electrode and a drain electrode, it may react with a silicon (Si) film that is used as a buffer. Therefore, when copper is applied to a gate electrode, a source electrode, and/or a drain electrode, it cannot be used as a single layer but is used as a copper/titanium or a copper/titanium alloy by disposing a barrier metal such as titanium (Ti) beneath it.
The copper/titanium or copper/titanium alloy is treated with a photolithography process and an etching process to form a wire and an electrode. A copper (Cu) layer as a first gate metal layer is deposited on a substrate. Then, a titanium (Ti) layer or a titanium alloy layer as a second gate metal layer is deposited on the first gate metal layer. Then, the second gate metal layer is selectively patterned to form a second gate pattern, and the first gate metal layer is selectively patterned to form a first gate pattern.
The patterning process of the first and second gate metal layers is included in an etching process. The first gate metal layer and the second gate metal layer are separately etched.
When copper/titanium or a copper/titanium alloy is not simultaneously but is separately etched, the fabrication process not only becomes complex, but also its yield rate may be deteriorated. The present embodiments overcome the above problems as well as provide additional advantages.